MySQL supports all of the standard SQL numeric data types. These
types include the exact numeric data types
(INTEGER
,
SMALLINT
,
DECIMAL
, and
NUMERIC
), as well as the
approximate numeric data types
(FLOAT
,
REAL
, and
DOUBLE PRECISION
). The keyword
INT
is a synonym for
INTEGER
, and the keyword
DEC
is a synonym for
DECIMAL
. For numeric type storage
requirements, see Section 10.5, “Data Type Storage Requirements”.
The numeric types used for the results of calculations depends on the operations being performed and the numeric types of the operands; for more information, see Section 11.5.1, “Arithmetic Operators”.
As an extension to the SQL standard, MySQL also supports the
integer types TINYINT
,
MEDIUMINT
, and
BIGINT
. The following table shows
the required storage and range for each of the integer types.
Type | Bytes | Minimum Value | Maximum Value |
(Signed/Unsigned) | (Signed/Unsigned) | ||
TINYINT |
1 | -128 |
127 |
0 |
255 |
||
SMALLINT |
2 | -32768 |
32767 |
0 |
65535 |
||
MEDIUMINT |
3 | -8388608 |
8388607 |
0 |
16777215 |
||
INT |
4 | -2147483648 |
2147483647 |
0 |
4294967295 |
||
BIGINT |
8 | -9223372036854775808 |
9223372036854775807 |
0 |
18446744073709551615 |
Another extension is supported by MySQL for optionally specifying
the display width of integer data types in parentheses following
the base keyword for the type (for example,
INT(4)
). This optional display width may be
used by applications to display integer values having a width less
than the width specified for the column by left-padding them with
spaces. (That is, this width is present in the metadata returned
with result sets. Whether it is used or not is up to the
application.)
The display width does not constrain the
range of values that can be stored in the column, nor the number
of digits that are displayed for values having a width exceeding
that specified for the column. For example, a column specified as
SMALLINT(3)
has the usual
SMALLINT
range of
-32768
to 32767
, and values
outside the range allowed by three characters are displayed using
more than three characters.
When used in conjunction with the optional extension attribute
ZEROFILL
, the default padding of spaces is
replaced with zeros. For example, for a column declared as
INT(5) ZEROFILL
, a value of
4
is retrieved as 00004
.
Note that if you store larger values than the display width in an
integer column, you may experience problems when MySQL generates
temporary tables for some complicated joins, because in these
cases MySQL assumes that the data fits into the original column
width.
The ZEROFILL
attribute is ignored when a
column is involved in expressions or
UNION
queries.
All integer types can have an optional (nonstandard) attribute
UNSIGNED
. Unsigned values can be used when you
want to allow only nonnegative numbers in a column and you need a
larger upper numeric range for the column. For example, if an
INT
column is
UNSIGNED
, the size of the column's range is the
same but its endpoints shift from -2147483648
and 2147483647
up to 0
and
4294967295
.
As of MySQL 4.0.2, floating-point and fixed-point types also can
be UNSIGNED
. As with integer types, this
attribute prevents negative values from being stored in the
column. However, unlike the integer types, the upper range of
column values remains the same.
If you specify ZEROFILL
for a numeric column,
MySQL automatically adds the UNSIGNED
attribute
to the column.
Integer or floating-point data types can have the additional
attribute AUTO_INCREMENT
. When you insert a
value of NULL
(recommended) or
0
into an indexed
AUTO_INCREMENT
column, the column is set to the
next sequence value. Typically this is
, where
value
+1value
is the largest value for the
column currently in the table. AUTO_INCREMENT
sequences begin with 1
.
For floating-point data types, MySQL uses four bytes for single-precision values and eight bytes for double-precision values.
The FLOAT
and
DOUBLE
data types are used to
represent approximate numeric data values. For
FLOAT
the SQL standard allows an
optional specification of the precision (but not the range of the
exponent) in bits following the keyword
FLOAT
in parentheses. MySQL also
supports this optional precision specification, but the precision
value is used only to determine storage size. A precision from 0
to 23 results in a four-byte single-precision
FLOAT
column. A precision from 24
to 53 results in an eight-byte double-precision
DOUBLE
column.
MySQL allows a nonstandard syntax:
FLOAT(
or
M
,D
)REAL(
or M
,D
)DOUBLE
PRECISION(
.
Here,
“M
,D
)(
”
means than values can be stored with up to
M
,D
)M
digits in total, of which
D
digits may be after the decimal
point. For example, a column defined as
FLOAT(7,4)
will look like
-999.9999
when displayed. MySQL performs
rounding when storing values, so if you insert
999.00009
into a FLOAT(7,4)
column, the approximate result is 999.0001
.
MySQL treats DOUBLE
as a synonym
for DOUBLE PRECISION
(a nonstandard
extension). MySQL also treats REAL
as a synonym for DOUBLE PRECISION
(a nonstandard variation), unless the
REAL_AS_FLOAT
SQL mode is
enabled.
Because floating-point values are approximate and not stored as exact values, attempts to treat them as exact in comparisons may lead to problems. They are also subject to platform or implementation dependencies. For more information, see Section A.5.5.8, “Problems with Floating-Point Values”
For maximum portability, code requiring storage of approximate
numeric data values should use
FLOAT
or
DOUBLE PRECISION
with no
specification of precision or number of digits.
The DECIMAL
and
NUMERIC
data types are used to
store exact numeric data values. In MySQL,
NUMERIC
is implemented as
DECIMAL
. These types are used to
store values for which it is important to preserve exact
precision, for example with monetary data.
Through version 4.1, MySQL stores
DECIMAL
and
NUMERIC
values as strings, rather
than in binary format. One character is used for each digit of the
value, the decimal point (if the scale is greater than 0), and the
“-
” sign (for negative numbers).
When declaring a DECIMAL
or
NUMERIC
column, the precision and
scale can be (and usually is) specified; for example:
salary DECIMAL(5,2)
In this example, 5
is the precision and
2
is the scale. The precision represents the
number of significant digits that are stored for values, and the
scale represents the number of digits that can be stored following
the decimal point. If the scale is 0,
DECIMAL
and
NUMERIC
values contain no decimal
point or fractional part.
Standard SQL requires that the salary
column be
able to store any value with five digits and two decimals. In this
case, therefore, the range of values that can be stored in the
salary
column is from
-999.99
to 999.99
. In
versions up to and including 4.1, MySQL varies from this limit in
two ways due to the use of string format for value storage:
On the positive end of the range, the column actually can
store numbers up to 9999.99
. For positive
numbers, MySQL uses the byte reserved for the sign to extend
the upper end of the range.
DECIMAL
columns in MySQL before
3.23 are stored differently and cannot represent all the
values required by standard SQL. This is because for a type of
DECIMAL(
,
the value of M
,D
)M
includes the bytes
for the sign and the decimal point. The range of the
salary
column before MySQL 3.23 would be
-9.99
to 99.99
.
In standard SQL, the syntax
DECIMAL(
is
equivalent to
M
)DECIMAL(
.
Similarly, the syntax M
,0)DECIMAL
is
equivalent to
DECIMAL(
, where
the implementation is allowed to decide the value of
M
,0)M
. As of MySQL 3.23.6, both of these
variant forms of the DECIMAL
and
NUMERIC
data types are supported.
The default value of M
is 10. Before
3.23.6, M
and
D
both must be specified explicitly.
The maximum range of DECIMAL
and
NUMERIC
values is the same as for
DOUBLE
, but the actual range for a
given DECIMAL
or
NUMERIC
column can be constrained
by the precision or scale for a given column. When such a column
is assigned a value with more digits following the decimal point
than are allowed by the specified scale, the value is converted to
that scale. (The precise behavior is operating system-specific,
but generally the effect is truncation to the allowable number of
digits.)
When asked to store a value in a numeric column that is outside the data type's allowable range, MySQL clips the value to the appropriate endpoint of the range and stores the resulting value instead.
For example, when an out-of-range value is assigned to an integer
column, MySQL stores the value representing the corresponding
endpoint of the column data type range. If you store 256 into a
TINYINT
or TINYINT
UNSIGNED
column, MySQL stores 127 or 255, respectively.
When a floating-point or fixed-point column is assigned a value
that exceeds the range implied by the specified (or default)
precision and scale, MySQL stores the value representing the
corresponding endpoint of that range.
Subtraction between integer values, where one is of type
UNSIGNED
, produces an unsigned result by
default. If the result would otherwise have been negative, it
becomes the maximum integer value. If the
NO_UNSIGNED_SUBTRACTION
SQL mode
is enabled, the result is negative.
mysql>SET SQL_MODE = '';
mysql>SELECT CAST(0 AS UNSIGNED) - 1;
+-------------------------+ | CAST(0 AS UNSIGNED) - 1 | +-------------------------+ | 18446744073709551615 | +-------------------------+ mysql>SET SQL_MODE = 'NO_UNSIGNED_SUBTRACTION';
mysql>SELECT CAST(0 AS UNSIGNED) - 1;
+-------------------------+ | CAST(0 AS UNSIGNED) - 1 | +-------------------------+ | -1 | +-------------------------+
If the result of such an operation is used to update an
UNSIGNED
integer column, the result is clipped
to the maximum value for the column type, or clipped to 0 if
NO_UNSIGNED_SUBTRACTION
is
enabled.
Conversions that occur due to clipping are reported as
“warnings” for ALTER
TABLE
, LOAD
DATA INFILE
, UPDATE
, and
multiple-row INSERT
statements.
User Comments
MySQL Float and Real values do not appear to handle all the IEEE standard floating point representations such as NaN, and +/- Inf. Special accommodations are needed to avoid accidentally inserting 0's for these values when integrating a MySQL database with a scientific application that generates these values.
Using the MySQL.com search feature to look for documentation on the type BOOL, this page is the highest ranked Reference Manual page that comes up. However, the term does not even appear on the page.
According to the page headed "10.1.1. Overview of Numeric Types", BOOL and BOOLEAN are synonyms for TINYINT(1).
I thought I should include that fact on this page, since the page does come up when searching for it. (Fixing the search feature would be a better solution, though!)
bool deafulting to tinyint is not strict enough. if you really want bool type you should use type "bit(1)" which will allow you to use exactly 1 and 0 and maybe save space or use type "enum('T','F')" which will not save space but make it a true binary flag.
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